#include <Arduino.h> // Include Arduino core library for ESP32
#include <BLEDevice.h> // Include BLE library for ESP32
#include <BLEServer.h> // Include BLE server functionality
#include <BLEUtils.h> // Include BLE utility functions
#include <BLE2902.h> // Include BLE descriptor for notifications

// Define pins for components
#define LED_PIN 5 // GPIO 5 for LED (simulating vibration motor)
#define HRV_PIN 34 // GPIO 34 for potentiometer (simulating HRV sensor)
#define HRV_THRESHOLD 1500 // Threshold for low HRV (tweak based on testing)

// Define BLE service and characteristic UUIDs
#define SERVICE_UUID "4fafc201-1fb5-459e-8fcc-c5c9c331914b" // Unique service UUID
#define CHARACTERISTIC_UUID "beb5483e-36e1-4688-b7f5-ea07361b26a8" // Unique characteristic UUID

// Global BLE objects
BLEServer *pServer = NULL; // Pointer to BLE server
BLECharacteristic *pCharacteristic = NULL; // Pointer to BLE characteristic
bool deviceConnected = false; // Track BLE connection status

// BLE server callbacks to handle connection/disconnection
class MyServerCallbacks : public BLEServerCallbacks {
  void onConnect(BLEServer* pServer) { // Called when a device connects
    deviceConnected = true; // Set connection flag
    Serial.println("Device connected"); // Log connection
  }
  void onDisconnect(BLEServer* pServer) { // Called when a device disconnects
    deviceConnected = false; // Clear connection flag
    Serial.println("Device disconnected"); // Log disconnection
    BLEDevice::startAdvertising(); // Restart advertising
  }
};

void setup() {
  Serial.begin(115200); // Start serial communication at 115200 baud
  pinMode(LED_PIN, OUTPUT); // Set LED pin as output
  digitalWrite(LED_PIN, LOW); // Ensure LED is off initially
  pinMode(HRV_PIN, INPUT); // Set HRV pin as input (analog)

  // Initialize BLE
  BLEDevice::init("FocusNudger"); // Set BLE device name
  pServer = BLEDevice::createServer(); // Create BLE server
  pServer->setCallbacks(new MyServerCallbacks()); // Attach connection callbacks
  BLEService *pService = pServer->createService(SERVICE_UUID); // Create BLE service
  pCharacteristic = pService->createCharacteristic( // Create characteristic
    CHARACTERISTIC_UUID,
    BLECharacteristic::PROPERTY_READ | BLECharacteristic::PROPERTY_NOTIFY // Allow read and notify
  );
  pCharacteristic->addDescriptor(new BLE2902()); // Add descriptor for notifications
  pService->start(); // Start the service
  BLEAdvertising *pAdvertising = BLEDevice::getAdvertising(); // Get advertising object
  pAdvertising->start(); // Start advertising
  Serial.println("BLE advertising started"); // Log advertising start
}

void loop() {
  int hrvValue = analogRead(HRV_PIN); // Read analog value from potentiometer (0-4095)
  Serial.print("HRV: "); // Print label
  Serial.println(hrvValue); // Print HRV value

  if (hrvValue < HRV_THRESHOLD) { // Check if HRV indicates distraction
    digitalWrite(LED_PIN, HIGH); // Turn on LED (simulate vibration)
    delay(200); // Vibrate for 200ms
    digitalWrite(LED_PIN, LOW); // Turn off LED
    Serial.println("Vibration triggered"); // Log vibration
  }

  if (deviceConnected) { // If a device is connected via BLE
    String hrvStr = String(hrvValue); // Convert HRV to string
    pCharacteristic->setValue(hrvStr.c_str()); // Set BLE characteristic value
    pCharacteristic->notify(); // Notify connected device
    Serial.print("Sent HRV via BLE: "); // Log BLE transmission
    Serial.println(hrvStr); // Print sent value
  }

  delay(1000); // Wait 1 second before next loop
}